Recently, a system known as the Universal Product Code (UPC) has been developed as an aid to supermarkets, their suppliers and other retailers. The system includes the provision of a symbol on each packaged item or on the item itself. The symbol is optically machine readable and consists of plurality of spaced bars of various thicknesses and spacings. The bars are "read" by an appropriate optical scanner, for example, at a checkout counter of a retail store. Each product is assigned a symbol which has a different configuration of lines and spaces than all other products. Each symbol corresponds to a special number or alphanumeric code associated with each particular product. The scanner output is coupled to an electronic logic system which can perform a variety of functions. For example, the logic system can operate a cash register-receipt printout device to compute the price of an item and add it to the bill. It may also be used to maintain inventory control as well as to reprice items without requiring each item itself to be remarked with the new price.
It is intended that the standard overall size of the complete symbol will correspond approximately to that of a postage stamp. However, the actual overall size of the symbol will vary depending on the size of the particular product or its package. For example, the size of the symbol may vary from between 85 percent to 200 percent of the standard or nominal size. The bars of the symbol are relatively thin and, when the symbol is of nominal size, will vary from approximately 0.013 to 0.052 inch in width, each line being an integer multiple of 0.013 inch in width. It is critical that the width of each of the bars falls within the acceptable tolerances in order that the scanning system may function effectively. For example, with a symbol of standard size a tolerance of .+-.0.004 inch in the width of a bar presently is believed to be acceptable. The acceptable tolerance in the width of a bar may vary as the size of the symbol varies from the standard. For example, in a symbol which is twice the size of the standard size and in which the bar widths will be an integer multiple of 0.026 inch, the acceptable tolerance will be greater.
It is an object of the invention to provide a device to enable the widths of the bars and spaces in the printed symbol to be checked easily and quickly.